The guides and explanations for custom quest are currently being edited, thank you for your patience.
Custom Quest is an upcoming plugin for Unity. It aims to fulfill any needs a developer could have for a quest system, and will of course play a major role in another upcoming title, Quest Accepted.
Documentation (API) can be found here here.*
guides and explanations of use can be found menu on the left.
One of the major features of the system, is the ability to easily expand and customize each individual quest as needed. The user can even add new code, without touching the core!
It is planned to be released on the asset store in August.